#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=1e5+100;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
char str[maxn];
LL era[maxn];
LL solve(char A,char B){
    return min( abs((A-'a')-(B-'a') ) ,(A-'a'+1)+abs( ('z'-'a')-(B-'a') ) );
}
int main(void)
{
  LL n,p;n=read();p=read();
  cin>>(str+1);
  LL len=strlen(str+1);
  for(LL i=1;i<=len/2;i++){
        era[i]=era[len-i+1]=min( solve(str[i],str[len-i+1]),solve(str[len-i+1],str[i]) );
  }
  if(len){
    LL sum=0;
    if(p>len/2){
        LL pre=len;LL suf=len/2+1;
        for(LL i=len/2+1;i<=len;i++) {
                if(era[i]) suf=max(suf,i),pre=min(pre,i),sum+=era[i];
        }
        if(p>=suf) sum+=(p-pre);
        else if(p<=pre) sum+=(suf-p);
        else{
            sum+=min(abs(suf-p),abs(p-pre));
            sum+=(suf-pre);
        }
    }
    else{
        LL pre=len/2+1;LL suf=1;
        for(LL i=1;i<=len/2;i++){
            if(era[i]) suf=max(suf,i),pre=min(pre,i),sum+=era[i];
        }
        if(p>=suf) sum+=(p-pre);
        else if(p<=pre) sum+=(suf-p);
        else{
            sum+=min(abs(suf-p),abs(p-pre));
            sum+=(suf-pre);
        }
    }
    cout<<max(sum,(LL)0)<<"\n";
  }
  /*
  else{
    LL sum=0;
    if(p>len/2){
        LL pre=len;LL suf=len/2+1;
        for(LL i=len/2+1;i<=len;i++) {
                if(era[i]) suf=max(suf,i),pre=min(pre,i),sum+=era[i];
        }
        if(p>=suf) sum+=(p-pre);
        else if(p<=pre) sum+=(suf-p);
        else{
            sum+=min(abs(suf-p),abs(p-pre));
            sum+=(suf-pre);
        }
    }
    else{
        LL pre=len/2;LL suf=1;
        for(LL i=1;i<=len/2;i++){
            if(era[i]) suf=max(suf,i),pre=min(pre,i),sum+=era[i];
        }
        if(p>=suf) sum+=(p-pre);
        else if(p<=pre) sum+=(suf-p);
        else{
            sum+=min(abs(suf-p),abs(p-pre));
            sum+=(suf-pre);
        }
    }
    cout<<max(sum,(LL)0)<<"\n";
  }
    */
return 0;
}
